As we chat ahead of the release of his latest film, The Flood, he admits, “I don’t think I really knew that actors existed or what they did until I went to university.”
It was at Aberdeen University that he “just fell into” the world of drama.
“I didn’t have any notion that I wanted be an actor until a couple of my contemporaries at university who were involved in the drama society, encouraged me to give it a go,” he recalls.
Indeed, when Iain first applied to university, it was to study computer programming.
“The second time, I just studied English, which was wonderfully vague in it’s intention,” he laughs.
As a kid in the Capital, Iain reflects that performing was an alien world to his brother Hamish, now a respected theatre director, and himself.
“We began life in the Salisbury/Arthur’s Seat area,” he remembers, “then we moved to the Church Hill area in my mid-childhood.
“Arthur’s Seat was a bit of a playground for me, but it became more of one when the Commonwealth Pool landed. We always used to go there.
“I remember the grand opening and how exciting that was and, in the early days, any fool could jump off the high board, so I used to like doing that.”
Laughing, he adds, “Yes, diving off the top board at the risk of crippling myself was a great pleasure.”
With no ‘showbiz’ in the family, his road to the stage took a bit long than most.
“I’m probably forgetting to mention someone, but I think Hamish and I were probably kind of left-field and a worry at the time for our parents.
“My father worked for an Investment Trust, he began at a low level, stayed with them for many decades, and ended up at the top of the Scottish Investment Trust.
“My mother was an occupational therapist but gave up work to look after us boys. So there was no great drama or showbiz in the family.
“It was definitely an usual step to take.
“However, when I was doing my first play at university - Arthur Miller’s The Crucible, playing a relatively unimportant part - a couple of people, particularly a girl I really fancied, said, ‘I really believed you. You were good.’ That was all the encouragement I needed.
“To be honest, I just discovered that I really cared about it.
“I wanted to improve at it and suddenly, that whole world just opened up. then I was very lucky to go on and get into the Royal Academy of Dramatic Art (RADA), an affirmation that it might be something worth pursuing.”
That his passion for what he does remains to this day is evident as we turn our attention to The Flood, which is released on 21 June.
Described by Human Rights Watch as “an accurate portrayal of the refugee crisis,” The Flood is set in France and the UK and follows a hardened immigration officer who must uncover if a high-profile asylum seeker is lying and has a more sinister reason for wanting to come to the UK.
“It’s really is a very timely film,” says Iain, adding, “but we made it more than a year ago.
“It’s a worry that it is the sort of film that is hard to get distribution for because, as feature films go, it doesn’t have ‘commercial’ written all over it.”
It’s a film that Iain says he is particularly “proud to be a part of”, explaining, “It’s a very incisive and informative look at refugees and the difficulties they have to overcome to gain legal entry to the UK.
“It walks a very fine line to try and show everyone’s point of view and in doing that, looks at how over-taxed the Immigration Service is, meaning the odds are stacked against people who come with a legal claim.
He continues, “It’s a very human story and fair-minded look at the whole subject.
“It’s just not something that is easy to get up and running and funded, so I’ve got great admiration for the makers and their commitment.”
It’s a very different movie to the one that opened Iain’s eyes to the potential the world of cinema held for him.
In 1990 he played Hamlet in Tom Stoppard’s comedy drama Rosencrantz & Guildenstern Are Dead.
“It was filmed in the former Yugoslavia and Tom Stoppard remains a good friend,” he says.
“I had recently played Hamlet on stage at the Bristol Old Vic and I think he was aware of that, so got me to play the role on film.
“It was great fun. There was Gary Oldman, Tim Roth and myself and we had a ball doing it.
“It was early on in my career and introduced to the wonders of film; they take you away to all these places you wouldn’t necessarily go on holiday.
“That was when the draw of films started to dawn on me; I saw the possibilities outside of the stage, which was what I knew more of up to that point.”
Iain has since wracked up an impressive CV, Downton Abbey, Resident Evil: Extinction, Lara Croft: Tomb Raider and Doctor Who just some of a long list of credits.
Despite his travels, however, Edinburgh remains home, even though he has now lived in London longer than he ever did here.
“I have so many fond memories, it must have been that my formative years were spent in Edinburgh.
“I’ve lived in London since going to RADA in my very early 20s, yet still feel I know Edinburgh better.
“My parents are still there and in my mind I always imagined I get back, but I ended up marrying an English lady and, with the children, we are very grounded where we are.
“But we do come up three of four times a year to see my parents and I can get about in Edinburgh in a way I never could in London - we even get back on the buses in Edinburgh - and my children love coming to Edinburgh too.”
With a smile he adds, “...and one of their favourite haunts is the Commonwealth pool.”
The Flood is in UK cinemas and on demand from 21 June